Dihydroxyacetone Production in the Nectar of AustralianLeptospermumIs Species Dependent

Abstract

This study is the first large-scale survey of the presence of dihydroxyacetone (DHA) in the nectar of the Australian Leptospermum tree species. The work undertaken supports the growing global demand for bioactive Leptospermum honey. Leptospermum honey derived from L. scoparium in New Zealand, also referred to as Ma ̅ nuka honey, has a reputation for wound-healing and antimicrobial properties, which is based on its methylglyoxal (MGO) content. High-DHA nectar correlates to high-MGO honey, but not all Leptospermum species produce DHA in their nectar. This study investigates 55 of the 84 Leptospermum species native to Australia for their DHA-producing capability, with the DHA to total sugar (DHA:Tsugar) ratio of nectar samples determined by HPLC-PDA. DHA:Tsugar ranged from nondetectable in L. laevigatum, L. coriaceum, and L. trinervium to >16 000 mg/kg in L. speciosum and L. whitei. High-DHA Leptospermum species were identified for beekeepers to target for honey production and plantation development.

Nectary photosynthesis contributes to the production of mānuka (Leptospermum scoparium) floral nectar

“…Whilst the results presented here provide evidence for a link between nectary photosynthesis and nectar sugars, an origin for nectar DHA from within nectary triose‐phosphate pools still requires an explanation for how DHAP is dephosphorylated to form DHA. Furthermore, why is DHA only observed as a measurable component of nectar within a sub‐clade of the Leptospermum genus (Norton et al ., 2015; Williams et al ., 2018), rather than all species with green nectaries? Nectary photosynthesis could be a more significant contributor to nectar flow in these species, or it is possible that members of this Leptospermum clade share an allele for a phosphatase with higher‐than‐normal activity towards DHAP (Fig.…”

“…1). In addition to fructose, glucose and sucrose, the floral nectar of mānuka and a subset of other Leptospermum species contains small amounts of dihydroxyacetone (DHA) (Williams et al ., 2018), a three carbon sugar that is the precursor of the nonperoxide antibacterial activity of mānuka honey (Adams et al ., 2008; Mavric et al ., 2008; Adams et al ., 2009). The DHA content of mānuka nectar is highly variable, with some of this variation attributed to plant genotype, flower stage of development, temperature, and differential resorption of nectar components (Williams et al ., 2014; Clearwater et al ., 2018; Smallfield et al ., 2018; Noe et al ., 2019).…”

Micropropagation of the therapeutic-honey plants

“…M anuka honey contains high levels of the antimicrobial and wound-healing compound, methylglyoxal (MGO), which is converted gradually in the honey from dihydroxyacetone (DHA) that is found in L. scoparium nectar (Carter et al 2016;Cokcetin et al 2016;Grainger et al 2016;Niaz et al 2017;Schmidt et al 2021). Honeybees that forage on L. scoparium and some other Leptospermum species in Australia also produce honey that contains high levels of MGO (Cokcetin et al 2016;Pappalardo et al 2016;Williams et al 2018). Demand for therapeutic MGO-containing honey is greater than supply, so there is a drive to establish Leptospermum plantations to provide nectar for therapeutic honey production.…”

WITHDRAWN: Development of a robust method for propagation of Leptospermum scoparium J.R.Forst. & G.Forst. from semi-hardwood cuttings

“…Leptospermum scoparium (Manuka) honey has non-hydroxide antibacterial properties largely due to the presence of methylglyoxal (MGO) (5). The precursor to MGO is dihydroxyacetone (DHA) and is found in the nectar of L. scoparium plants (6)(7)(8)(9). Plants with high DHA to total sugars (DHA:Tsugar), in the nectar, are believed to produce honeys with the highest MGO concentration (6,7).…”

“…To ensure economical production of high quality bioactive honey, plantations should focus on using plant selections with high levels of DHA:Tsugar, excellent ower production and high nectar ow (2,8,10). Williams,King (9) and Williams,Pappalardo (8) found the production of DHA to total sugars to be variable within and across both wild and cultivated populations of L. scoparium in New Zealand and Australia.…”